1. Field of Invention
The present invention generally relates to optical devices wherein one or more movable lenses are provided for focusing an image of an object in a preselected plane. More particularly, the invention relates to an improved focusing coupler capable of varying the field of view and magnification, and to a viewing system utilizing the same, for use by surgeons in endoscopically viewing internal, "closed", surgical sites.
2. Summary of the Prior Art
Endoscopes are medical devices which are used to provide external images of organs and structures within a human or animal. As used herein, the term "endoscope" includes, but is not limited to, arthroscopes, colonoscopes, bronchoscopes, hysteroscopes, cystoscopes, sigmoidoscopes, laparoscopes and urethrascopes.
Typically, endoscopes comprise an insertion portion in the form of a hollow shaft that is designed for insertion through a body orifice or a small incision into an internal body cavity. An objective lens unit consisting of one or more lenses is mounted within the shaft at its forward (distal) end. The objective lens unit forms an image of the area that is viewed by it, i.e., the "target". The image of the target so captured is then transmitted to an optical viewing device or to an electronic imaging device. The hollow shaft may, but need not, include optical image transmission apparatus, e.g., a relay lens, for applying the image to the optical viewing device or to the electronic imaging device.
A conventional optical endoscope provides an optical viewing capability in the form of an eyepiece unit that is affixed to the proximal (rear) end of the shaft. The eyepiece unit is nominally focused to infinity for direct viewing of the image by the surgeon. More specifically, the objective lens unit of a conventional optical endoscope is usually designed so as to form a focused image of an object or other target located at a predetermined target distance therefrom. That predetermined object distance is the object position relative to the objective lens unit which is thought by the designer to be most frequently required by a surgeon. Further, the overall optics system of a conventional optical endoscope is designed so that the image beam emerging from the eyepiece unit is collimated, i.e., focused nominally to infinity. The cornea of the surgeon's eye acts to focus the collimated image beam on the retina of the surgeon's eye during direct viewing of the image by the surgeon.
Another type of endoscope is an integrated video endoscope that incorporates a video camera. As used herein, the term "video camera" is used to designate a solid state, electronic imaging device, preferably in the form of a charge coupled device ("CCD"). More particularly, in the typical integrated video endoscope, the CCD or other solid state imaging device is mounted within the hollow endoscope shaft, or in a housing that is attached to the proximal end of the hollow shaft. The electronic imaging device generates electrical signals representative of the images received from the objective lens unit. Those signals then are processed to generate video signals which are used to create a video display on a conventional TV monitor or a head-mounted video display unit. In this connection, it should be noted that in addition to the CCD or other electronic imaging device, the camera may comprise one or more circuits for controlling the operation of the CCD and processing the CCD's output signals.
It also should be noted that many endoscopes are known which have stereoscopic capabilities. In such endoscopes, the optics are designed so as to generate first and second images of the target, with each image being taken from a different angle. The two images either may be viewed directly by a stereo (binocular) eyepiece unit, or they may be transmitted to an electronic imaging device for generating signals that in turn are used to generate a stereoscopic video display according to known techniques. The depth perception provided by such electronically generated stereo images is valuable to a surgeon in conducting a surgical procedure within a "closed" surgical site.
The present state of the art regarding endoscopic systems is exemplified by the teachings and disclosures of the following United States patents and patent applications: U.S. patent. application Ser. No. 08/722,724 filed Oct. 1, 1996 by K Hori et al; U.S. Pat. No. 5,538,497 issued Jul. 23, 1996 to K Hori; U.S. Pat. No. 5,582,576 issued Dec. 10, 1996 to K. Hori et al.; U.S. Pat. No. 5,603,687 issued Feb. 18, 1997 to K. Hori et al.; U.S. Pat. No. 5,662,584 issued Sep. 2, 1997 to K. Hori et al.; U.S. Pat. No. 5,682,199 issued Oct. 28, 1997 to James D. Lankford; U.S. Pat. Nos. 5,673,147, 5,191,203, and 5,122,650, all issued to Harry R. McKinley; and U.S. Pat. No. 5,612,816, issued to Fritz Strahle; and the art cited during the prosecutions of those patents and applications The disclosures and teachings of the above-identified prior art are hereby incorporated by reference into this specification.
A conventional optical endoscope, whether monocular or stereo, may be converted to a video endoscope by attaching a video camera head to the endoscope in a position to receive the image beams passed by the eyepiece unit (as used herein the term "video camera head" designates a housing that contains a video camera and that is adapted to be connected to an endoscope directly or via an endoscope coupler). Such conversions are favored in the art. This is because a single video camera head may be used with many different endoscopes, thereby providing significant cost savings over the alternative of providing an integrated video endoscope for each type of surgical procedure. However, since the exit image beam of the conventional eyepiece unit is generally collimated, and since the target distance will vary as the endoscope is manipulated by the surgeon, it is desirable to provide a focusing device between the video camera head and the conventional optical endoscope so that the image beam passed by the eyepiece unit can be focused so as to accommodate a wide range of object distances. The use of such a focusing device has the effect of changing the magnification, and hence the field of view, of the image, while keeping the image properly focused on the camera image plane or the surgeon's retina.
Heretofore, focusing couplers have been available which include a focusing lens unit mounted for reciprocal movement within a coupler housing, and a manually movable actuating means located outside of the housing which is mechanically or magnetically coupled to the focusing lens unit for moving that unit so as to focus the image beam on the image plane of the CCD or other electronic imaging device of a video camera. Examples of such prior art couplers are provided by U.S. Pat. No. 5,359,992, issued Nov. 1, 1994 to K. Hori et al and U.S. Pat. No. 5,056,902, issued Oct. 15, 1991 to R. B. Chinnock et al, and the prior art listed in those patents.
All such externally operable focusing couplers provided for use with conventional optical endoscopes are characterized by several disadvantages. For example, to the extent that such focusing couplers involve externally movable elements having closely fitting surfaces, such as manually rotatable focusing rings, the areas between the closely fitting surfaces provide small volumes into which micro-organisms can enter. These small volumes are often referred to in the art as "bug traps", and are to be avoided whenever possible because they present sterilization problems. Also, such manually focused devices require the use of a surgeon's hand, which in turn may require the surgeon to divert his attention from the surgical procedure being performed and/or the video display of the surgical site. Further, manually operable focusing couplers are not adapted for use with autofocusing controls.